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Intermediate Tutorial 6

In the first of two tutorials about the different types of lens available for interchangeable system cameras, we discover the many glass elements in a lens assembly and look at the standard kit lens that came with your camera and the difference between zoom and fixed focal length lenses.

6

Interchangeable Lenses Explained – Part One

In photography, the lens used is key to the end result. Lenses are largely responsible for the quality as well as the artistic look of a photograph. Light entering the camera passes through the many glass elements that make up the lens assembly. We talk about fitting ‘the lens’ – but actually there may be up to 20 lens elements combining to make the complete unit. So, any distortion, discolouration or reduction of brightness introduced by imperfections in any one will affect the image before the sensor or processor even has a chance to do its job.

Amongst the many lens elements is the Image Stabilisation lens assembly that counteracts small movements of the camera

Despite a huge variation in their construction, one way system camera lenses are all described is in terms of their Focal Length. Generally given in millimetres, this refers to the distance from the Focal Plane (usually the image sensor) to the point where light rays from the lens converge. Lenses with a wide angle of view have a short focal length, whereas those with a narrow angle of view – typically telephoto lenses – have a long focal length. See diagram below for reference.

Types of lens

Lenses are normally grouped into categories depending on their focal length/angle of view:

Ultra Wide Angle

Wide Angle

Standard

Telephoto

Super Telephoto

There are also lens sub-groups within these categories – Fixed Focal length, Zoom, Macro, Fast and Ultra-fast. Over two tutorials in this module, we will cover off what these types of lenses do and suggest some shooting situations where they could be preferred.

Note – lens manufacturers use different focal length calculations, but for simplicity we will refer to lenses by their equivalent 35mm focal length.

Let’s start with the most common – usually the one supplied with the camera…

Standard kit lens

The chances are you purchased your camera complete with a general-purpose zoom lens. These, so called, kit lenses are a very good way to get started with your new purchase.

The ‘standard’ focal length range falls between 45mm and 75mm, meaning this lens group contains the focal length closest to the normal human field of view – about 50mm.

Kit lenses, however, usually cover a range slightly larger, typically 28-90mm. This means that at the wide end they can be used for group shots, indoors or outdoors, and at the telephoto end they can be used to help get you a little closer to your subject.

One advantage of shooting with a standard lens is that a 50mm focal length gives a very ‘natural’ field of view, and objects with straight vertical lines will be true and undistorted.

A good use for the standard 50mm focal length is the classic wedding group shot shown right – provided you can stand far enough back to fit everyone in.

The LUMIX H-FS1442A kit lens

Photo taken by cjthespringer

Telephoto and Super-telephoto

75-350mm lenses fall into the Telephoto category and are generally used for shooting where it is difficult to get close to a subject. The Angle-of-View is narrow, therefore enlarging the subject on the sensor – making it appear much closer than it actually is. Telephoto lenses are not only good for picking out distant scenes and getting in close to elusive subjects, such as wildlife, they also do cool things to the perspective and depth of field.

Take for instance these two shots below.

The first image was shot with 50mm focal length, whereas the second was shot from further back, but zoomed in – using 200mm. Notice how the subjects remain the same size in the frame, but the long focal length has foreshortened the background. Adding further interest, if your subject is relatively close to the background, the depth of field being shallower in the telephoto lens will give it a nice soft-focus effect.

50mm focal length

200mm focal length

Super-telephoto lenses have a focal length over 350mm and are usually used by specialists in wildlife or sports photography. Due to the number of lens elements and huge magnification, they can be very long and heavy. The longer the lens, the greater the drop off of light, so maintaining good f stop performance requires larger diameter lenses with high-accuracy glass – which is often reflected in the price!

600mm focal length

It can be very exciting shooting with a 400, 600 or even 1000mm lens… but be sure to have a strong tripod and large kit bag to carry it around.

On the other hand, the smaller body and sensor size of the Lumix G system means that you can save a huge amount of space and weight with the Micro Four Thirds compact super-telephoto lenses, but more of that later.

Zoom or fixed focal length?

A popular choice for the casual photographer is the zoom lens – with the advantage of covering a range of focal lengths in one unit. However, this convenience is sometimes at the cost of optical quality compared to the best fixed lenses.

The zoom function means the focal length is changed by moving optics inside the barrel, giving you the option to shoot from wide angle to telephoto without changing your lens. Sometimes they are referred to by their magnification or zoom ratio – 3x, 5x, 10x etc. – worked out by dividing the longest focal length by the shortest, so a 28-280mm lens is a 10x zoom.

The LUMIX H-FS14140 10x super zoom lens

The LUMIX H-FS14140 10x super zoom lens (right), for example, offers a range of focal lengths from wide angle to high telephoto. With ‘Power OIS’, even night-time shots at slow shutter speeds are sharper than ever before, and the near-silent linear motor auto-focus system is perfect for shooting video.

Fixed focal length lenses, sometimes referred to as ‘prime lenses’, offer one focal length of course. Without any additional moving elements, their optical qualities are generally superior and, as such, they are favoured by professionals. Often offering a wider aperture, they are therefore ideal for high shutter speed shooting, or where shallow depth of field is desired.

Whether you choose a zoom or a prime lens, always remember: the greater the focal length, the harder it will be to hold the camera still and avoid blurring the shot. So, use a sturdy tripod wherever possible, or select a shutter speed fast enough to freeze the movement.
The rule of thumb is: minimum shutter speed = focal length, so for a 250mm lens, shoot at 1/250th sec.

The LUMIX Advantage

LUMIX lenses for Panasonic’s Micro Four Thirds digital camera system offer the advantage of being designed, from conception, specifically for the digital camera era. Optimised in size to present light at a perpendicular angle to the sensor, they deliver outstanding performance in a compact and lightweight form that offers a real alternative to bulky traditional DSLR lenses.

The LUMIX H-PS14042 was the World’s first Power Zoom option for interchangeable lens cameras. Here, it is compared to the already compact standard 14-42mm zoom lens – and you can see how it set new standards for ultra-compact lenses.

LUMIX Micro Four Thirds lenses offer a great saving in size and weight

Also shown is the LUMIX MFT lens line-up compared in size with traditional DSLR lens equivalent models, including wide-angle, macro and super wide-angle lenses – which we’ll be looking at in the next tutorial.